VARIATION IN RESPONSE TO SYNTHETIC LUTEINIZING HORMONE—RELEASING HORMONE (LH‐RH) AT DIFFERENT PHASES OF THE SAME MENSTRUAL CYCLE IN NORMAL WOMEN

Summary Synthetic luteinizing hormone‐releasing hormone (LH‐RH) was given intravenously in a dose of 100μg. to 24 normal regularly menstruating women at various stages of the same menstrual cycle. The luteinizing hormone (LH) response was always greater during the luteal phase (days 22 to 24) than during the early follicular (days 4 to 6) or mid‐follicular phases (days 8 to 10). No statistical difference was shown between the two groups studied in the early and mid‐follicular phases for LH release, but in four subjects, studied on four occasions in the same cycle, the greatest release of LH occurred on day 14. The follicle stimulating hormone (FSH) responses were more variable although every patient showed a significant rise in circulating FSH after the injected LH‐RH. The luteal phase response was greater in all but four of the subjects tested. However, a significantly larger response (0.1 0.05) was seen in the early follicular phase when compared with the mid‐follicular phase responses. No correlation between LH or FSH responses and circulating progesterone levels could be demonstrated in any of the subjects. A negative correlation (r=−0.55; 0.1>p>0.05) was found between sum of FSH increments and circulating oestradiol during the early follicular phase, but no such correlation was seen in the mid‐follicular phase responses. Similarly, a negative correlation between sum of FSH increments and oestradiol (r=−0.70; 0.05>p>0.02) was demonstrated in the luteal phase responses, but no correlation with LH response was apparent.